1. Field of the Invention
The present invention relates to telecommunications, and more particularly, to wireless and wireline communications.
2. Description of the Related Art
Wireless communications systems provide wireless service to a number of wireless or mobile units situated within a geographic region. The geographic region supported by a wireless communications system is divided into spatially distinct areas commonly referred to as “cells.” Each cell, ideally, may be represented by a hexagon in a honeycomb pattern. In practice, however, each cell may have an irregular shape, depending on various factors including the topography of the terrain surrounding the cell. Moreover, each cell is further broken into two or more sectors. Each cell is commonly divided into three sectors, each having a range of 120 degrees, for example.
A conventional cellular system comprises a number of cell sites or base stations geographically distributed to support the transmission and reception of communication signals to and from the wireless or mobile units. Each cell site handles voice communications within a cell. Moreover, the overall coverage area for the cellular system may be defined by the union of cells for all of the cell sites, where the coverage areas for nearby cell sites overlap to ensure, where possible, contiguous communication coverage within the outer boundaries of the system's coverage area.
Each base station comprises at least one radio and at least one antenna for communicating with the wireless units in that cell. Moreover, each base station also comprises transmission equipment for communicating with a Mobile Switching Center (“MSC”). A mobile switching center is responsible for, among other things, establishing and maintaining calls between the wireless units, between a wireless unit and a wireline unit through a public switched telephone network (“PSTN”), as well as between a wireless unit and a packet data network (“PDN”), such as the Internet. A base station controller (“BSC”) administers the radio resources for one or more base stations and relays this information to the MSC.
When active, a wireless unit receives signals from at least one base station over a forward link or downlink and transmits signals to at least one base station over a reverse link or uplink. Several approaches have been developed for defining links or channels in a cellular communication system, including time-division multiple access (“TDMA”), orthogonal-frequency division multiple access (“OFDMA”) and code-division multiple access (“CDMA”), for example.
In TDMA communication systems, the radio spectrum is divided into time slots. Each time slow allows only one user to transmit and/or receive. Thusly, TDMA requires precise timing between the transmitter and receiver so that each user may transmit their information during their allocated time.
In a CDMA scheme, each wireless channel is distinguished by a distinct channelization code (e.g., spreading code, spread spectrum code or Walsh code). Each distinct channelization code is used to encode different information streams. These information streams may then be modulated at one or more different carrier frequencies for simultaneous transmission. A receiver may recover a particular stream from a received signal using the appropriate channelization code to decode the received signal.
In OFDMA systems, a carrier signal may be defined by a number (e.g., 1024) of sub-carriers or tones transmitted using a set of mathematically time orthogonal continuous waveforms. Each wireless channel may be distinguished by a distinct channelization tone. By employing orthogonal continuous waveforms, the transmission and/or reception of the tones may be achieved, as their orthogonality prevents them from interfering with one another.
For voice applications, conventional cellular communication systems employ dedicated links between a wireless unit and a base station. Voice communications are delay-intolerant by nature. Consequently, wireless units in wireless cellular communication systems transmit and receive signals over one or more dedicated links. Here, each active wireless unit generally requires the assignment of a dedicated link on the downlink, as well as a dedicated link on the uplink.
With respect to real-time and/or circuit switched services, such as voice, video and wireless gaming applications, for example, conventional cellular communication systems employ dedicated channels or links between a wireless unit(s) and a base station. Voice communications and other real-time and/or circuit switched services have to date been viewed as delay-intolerant by nature. Consequently, wireless units in wireless cellular communication systems transmit and receive signals over one or more dedicated links. Here, each active wireless unit generally requires the assignment of a dedicated link on the downlink as well as a dedicated link on the uplink.
The explosive growth of the Internet and private Intranets has resulted in increasing infrastructure supporting Internet Protocol (“IP”) transmission and reception. This explosion has led the wireless telecommunication equipment suppliers to reexamine assumptions regarding voice and data transmission. Employing an IP scheme for wireless telephony may simplify equipment designs, given the ease in which data and voice may flow interchangeably. Consequently, there is a move afoot to develop IP based wireless equipment capable of voice and data transmission/reception supportive of wireless cellular standards, such as 3 G, as well as other wireless standards, including those involving Wireless Fidelity (e.g., WiFi or 802.x).
The Internet is a packet-switched based architecture, where data transmitted over the network may be segmented and conveyed in packets. Unlike circuit-switched networks, such as the public switched telephone network (“PSTN”), a packet-switched network is connectionless—in other words, the dedicated end-to-end path of the packet-switched network is not required for each transmission. Rather, each router may calculate a preferred routing for a packet given current traffic patterns, and may send the packet to the next router. Thus, even two packets from the same message may not travel the same physical path through the network. This method is a type of layer three forwarding known as dynamic routing.
An IP packet is comprised of a packet data portion and an IP header. The IP header is comprised of a variety of header fields, including a source address and a destination address. The IP header, and therefore those fields which comprise the IP header, represent a transmission overhead since header bits are transported along with the actual data bits for each packet. Additionally, since IP routers forward IP packets based on each packets destination address, each IP packet header must be parsed at a controlling microprocessor in each router through which a packet is forwarded. The destination address associated with each respective packet is accessed by the microprocessor and a forwarding lookup table is utilized to forward each packet to a next router. Despite advances associated with processor speeds, the performance of forwarding algorithms and functions at each IP router utilizes precious router processing capacity and consequently limits the forwarding capacity of the routers.
In developing an IP based wireless equipment using a packet switching scheme capable of voice and data transmission/reception, various considerations require examination. Performing voice over an IP based system (e.g., VoIP) is, to date, a relatively low data rate application. To reduce the protocol and physical layer overhead in a VoIP design, the IP packets may be aggregated into relatively larger packets and transmitted using a single medium access control/physical layer frame (e.g., “MAC/PHY” frame). These IP packets may be aggregated over a fixed duration—e.g., 100 ms—of voice samples and packaged into a single physical layer frame.
Referring to FIG. 1, an example of a known voice frame aggregation scheme of having a fixed duration is shown. Here, the voice frame is aggregated over 40 ms, for example. From the depicted voice frame aggregation scheme, it is assumed that two frames each containing 20 ms voice samples, for example, are packaged together. One set of header information may be added to the aggregated frame and transmitted in a single physical layer frame. The header information may consist of one or more of the following: Real Time Transport (“RTP”); User Datagram Protocol (“UDP”) header; Internet Protocol (“IP”) header; Point-to-Point Protocol (“PPP”) header; Radio Link Protocol (“RLP”) header; Medium Access Control (“MAC”) header; Cyclic Redundancy Check (“CRC”); and physical layer tail bits used in channel coding.
Various problems, however, may arise when employing a voice frame aggregation of a fixed duration. Packet delay jitter, for example, may arise in a voice frame aggregation scheme of fixed duration if the data rate of the channel changes (e.g., the channel conditions vary between a wireless unit and an associated base station). By logical extension, as channel conditions vary, so to do available data rates. Longer packet transmission times may, for example, give rise to packet delay jitter when the channel data rate decreases. Here, the channel data rate may also decrease for reasons including variable conditions in the wireless channel. Larger delays may also be anticipated for the first aggregated packet generated at the beginning of an ON period for a wireless unit. This may transpire because the resources have been released during the wireless unit's OFF period and additional access delay may also be applied to the packet itself. Finally, voice frame aggregation of a fixed duration may be inefficient in its use of channel bandwidth.
Consequently, a demand exists for a method of frame aggregation that reduces packet delay jitter and the delay for the first aggregate pack, as well as increases the efficient use of the channel bandwidth.